JP2023546080A - Catalyst bed containing particulate photocatalytic catalyst - Google Patents

Abstract

The present invention relates to catalyst beds containing specific photocatalytic catalysts. The bed comprises structured particles b made of an inorganic material in combination with at least one semiconductor material a having photocatalytic properties, the combination comprising structured particles b made of an inorganic material; and/or - chemical or physicochemical deposition of the semiconductor material a on structured particles b made of inorganic material, the structured particles b It has a substantially spherical shape and an average diameter of 22 nm to 8.0 μm.

Description

The present invention relates to the field of photocatalysis and is aimed at treating a liquid or gas phase by contacting it with a photocatalytic material, which will be irradiated with a light source emitting in a suitable wavelength range. The present invention relates more particularly to a new type of photocatalytic material, a method for its preparation and its uses.

Photocatalysis is based on the principle of activation of semiconductors that act as photocatalysts using the energy provided by light irradiation. Semiconductors are characterized by their bandgap, ie, the energy difference between their conduction band and their valence band, which is characteristic of semiconductors. Photocatalysis can be defined as the absorption of photons, the energy of which is greater than the bandgap width between the valence band and the conduction band, which in the case of semiconductors induces the formation of electron-hole pairs. do. There is excitation of electrons into the conduction band and formation of holes on the valence band. This electron-hole pair allows the formation of free radicals, which can react with compounds present in the medium and initiate oxidation/reduction reactions, or alternatively by various mechanisms. will be recombined accordingly. Any photon with energy greater than the bandgap can be absorbed by the semiconductor. Photons with energy lower than its bandgap cannot be absorbed by the semiconductor.

The fields of application are vast: photocatalysis is therefore used to manipulate the decontamination of gaseous media, in particular the conversion of compounds of the type VOC (Volatile Organic Compounds) by oxidation. It can be used to treat liquid media such as those containing toluene, benzene, ethanol or acetone. Photocatalysis can also be used to convert CO ₂ in gaseous media by reduction into upgradeable compounds, especially those with one or more carbons, such as CO, methane, methanol, carboxylic acids. , converting it into ketones or other alcohols: CO ₂ is therefore actively converted rather than being captured and stored to reduce its content in the atmosphere. It is also possible to carry out photolysis of water in liquid or gaseous media to produce upgradable hydrogen H2, especially as a low carbon energy source.

A photocatalytic material in the form of a porous monolith is known from US Pat. The photocatalytic material is a refractory selected from silica, alumina or silica-alumina, with an amount of TiO ₂ ranging from 20% to 70% by weight relative to the total weight of the monolith and from 30% to 80% by weight relative to the total weight of the monolith. oxide, has a bulk density of less than 0.19 g/mL, and has a certain porosity, in particular with respect to macroporosity and mesoporosity. This would therefore be obtained in a material consisting entirely of titanium oxide, combining the semiconductor (titanium oxide) that is the source of its photocatalytic properties with one or two refractory oxides. It also relates to a material having a certain porosity which results in better photocatalytic performance qualities than those described above.

The subject of the present invention therefore lies in the development of improved photocatalytic materials, in particular in which the performance qualities of the photocatalyst are further improved and the implementation and/or production further improved.

International Publication No. 2018/197432

(Summary of the invention)
The invention relates, first of all, to a catalyst bed comprising particulate photocatalytic catalysts, said bed comprising structured particles b made of mineral material, said structured particles having at least one particle having photocatalytic properties. a semiconducting material a, the combination comprising: mixing structured particles b made of a mineral material with a semiconducting material a in the form of particles, and/or made of a mineral material produced by chemical or physicochemical deposition of semiconductor material a on structured particles b;
The structured particles b are essentially spherical and have an average diameter of 22 nm to 8.0 μm, preferably 30 nm to 7.5 μm.

The mineral material to which the present invention is directed is of the electrical insulator type and is therefore essentially inert towards photocatalysis: it is a material with a bandgap greater than 6 eV.

Preferably, this catalyst bed is intended to be a fixed bed (in particular as opposed to a fluidized bed).

The present invention therefore provides a solution to the problem in mineral materials that are not semiconductor materials, depending on the range of wavelengths targeted for irradiation of the semiconductor material, which allows the generation of electron-hole pairs and thus the desired photocatalytic reaction. We chose to disperse the semiconductor material by calibrating the size of the particles of this mineral material. This means that traditionally, in the field of photocatalysis, radiation sources are chosen in the UV-A, UV-B and/or visible range, with wavelengths capable of activating conventional semiconductor materials, e.g. titanium oxide. This is to define the range.

As a matter of fact, the present invention provides a method of directing radiation preferentially in the direction of the incident radiation by choosing particles (herein referred to as structured particles) made of mineral material that are spherical and have a certain average diameter. We exploit what is known under the term Mie scattering by causing an optimal scattering of: Mie scattering is directly related to the wavelength of the incident radiation, with a radius of 0.1 of the wavelength in question. shows preferential scattering of radiation at its axis of incidence for a spherical particle that is ~10 times larger. The structured particles of the invention have their suitably adjusted diameter and therefore amplify the effectiveness of irradiation in the range from UV-A radiation to the visible range: they It will scatter the radiation mainly in the direction of incidence from the surface of the bed, thereby significantly increasing the possibility of irradiation of the semiconductor material and thus improving its photocatalytic ability. This is because the penetration depth of the incident radiation within the catalyst bed is deeper, allowing the radiation to reach areas of the semiconductor material that are difficult for the radiation to reach.

Compared to materials that are similarly constructed but have particles outside this diameter range and/or that are non-spherical, the photocatalytic performance quality of the material is doubled, in fact three or four times more Even more in practice, it has been discovered that improvements of ten times or more can be achieved in the most preferred configurations, giving great flexibility in the implementation of the invention. Thus, depending on whether you prioritize the performance quality or cost of the catalyst, you can either amplify the performance quality of the material as much as possible with the same amount of semiconductor, amplify it to a lesser extent, or It is possible to choose to reduce the amount of semiconductor inside and keep it at least the same.

The present invention provides two alternative or cumulative variations for configuring the material, both of which have their advantages;
Variations with two types of particles, structured particles and semiconducting particles, are advantageous because they are simple to manufacture, do not require the integration of two types of materials, and because they are easy to prepare. This is because it is based only on a mixture of two types of powder and does not involve chemical reactions, heat treatment, etc. This modification also allows very easy adaptation to any shape and any size of the catalyst bed. Thereby, in situ, directly in the reactor in which the bed has to be placed, it is possible to easily adjust the ratio between two types of particles on a case-by-case basis, without prior pre-conditioning. It is possible to form a bed by adapting the granules, except by providing a suitable device to ensure as homogeneous a mixing as possible between the two types of particles. It is also possible to prepare the mixture beforehand so that only one product is deposited to form a bed.

Other variants consisting of chemical/physicochemical deposition of semiconductors onto structured particles also show advantages: a controlled distribution of the semiconductors, which favors the interaction of the two materials between them. in particular with respect to the radiation scattered by the particles in this case. In this way, it provides a "ready to use" product for forming the catalyst bed in the reactor. It should be noted that the structured particles can be completely or only partially covered by the semiconductor. It should also be noted that according to this variant, provision can also be made for a certain proportion of structured particles that remains free of deposition of semiconductor material.

Advantageously, the structured particles are (essentially) spherical and solid: their solidity gives them better mechanical properties, better mechanical strength, wear resistance. , provides wear resistance, etc.

Preferably, all of the particles within the bed are randomly arranged. This is because, surprisingly, this disordering was found to be beneficial regarding the photocatalytic performance quality of the material. The term "disordered" is understood to mean the fact that the particles of the material are not arranged in an orderly manner and do not form a layer of three-dimensionally ordered particles. The material according to the invention thus exhibits interparticle spaces of non-uniform size and position randomly arranged within the material. Furthermore, these spaces can be either a variant of a mixture of particles (of different sizes and shapes) or a variant with only one type of particle (a structured particle covered at least partially by a semiconductor). Depends on what's involved.

Preferably, if the bed contains the semiconductor material a in the form of particles, said particles exhibit an average size of at most 100 nm, in particular at most 50 nm, and at least 5 nm, preferably from 10 to 30 nm. It should be noted in this case that these particles are not, or necessarily not, spherical and their average size is not conditioned by the wavelength of the irradiating radiation.

Preferably, the catalyst bed according to the invention has a porosity equal to the ratio of the void volume in the photocatalyst bed to the total volume of the bed composed of voids and particles: a minimum of 40% and preferably a maximum of 80%, in particular from 40% It shows 70%. This porosity is indirectly an indicator of the disordered arrangement of the materials mentioned above. This is because the porosity is minimal when it comes to perfectly organized spheres, and the porosity according to the invention is greater than this minimum ratio.

Preferably, the catalyst bed according to the invention has a ratio of the volume occupied by structured particles b made of mineral material to the volume occupied by structured particles b made of semiconducting material(s) a, a' and of structured particles b made of mineral material. "Dilution factor" equal to the ratio of the volume occupied by the sum: maximum 80%, in particular 5% to 70%, preferably 10% to 50%. This dilution rate of up to 80% is chosen in particular when the semiconductor material a is chemically or physicochemically deposited onto structured particles b made from mineral materials, but it is understood that both variants of the invention It can be applied to

This term "dilution ratio" is used to reflect the proportion of active material (semiconductor) to structured particles that are a priori not at all or only slightly active. The higher the dilution rate, the greater the amount of structured particles. It will be seen from the examples below that this dilution rate can be increased without reducing, and in fact improving, the photocatalytic performance quality of the material as a whole. Insofar as the density of materials, especially semiconductors, can vary widely from semiconductor to semiconductor, it is more prudent to make inferences in terms of dilution by volume than by mass.

In one embodiment of the invention, the catalyst bed may include (at least) two different semiconductor materials, a first material a and a second material a'. It can be manufactured by:
- mixing structured particles b made of mineral material with semiconductor material(s) in the form of particles of a first material a and particles of a second material a', respectively; /or,
- chemical or physicochemical deposition of semiconductor material a, a' on carrier particles b; or by deposition of both a first semiconductor material a and a second semiconductor material a' on structured particles b; Deposition of a first semiconductor material a on a first part of structured particles b and a second semiconductor material a' on a second part of structured particles b.

Therefore, three powders of three different materials a, a' and b are to be mixed, namely two powders b+a and b+a' (covered by either the first semiconductor or the second semiconductor). There is either a single powder b+a+a' (structured particles covered by both the first and second semiconductor).

Naturally, it is possible to use more than two different semiconductor materials based on the same principle. There also remains the option of beds that additionally contain certain parts of the structured particles that are not covered by the semiconductor material, in a variant in which semiconductors are deposited on their surfaces.

Advantageously, the structured particles b made of mineral material may be made of metal oxide(s), in particular of metals of groups IIIa and IVa of the periodic table, preferably is selected from aluminum oxide, silicon oxide, and mixtures of aluminum oxide and silicon oxide.

Advantageously, the semiconductor materials a, a' and/or at least one of the semiconductor materials a, a' may be selected from inorganic semiconductors. The inorganic semiconductor may be selected from one or more elements of group IVa, for example silicon, germanium, silicon carbide or silicon-germanium. They also contain elements of groups IIIa and Va, such as GaP, GaN, InP and InGaAs, or elements of groups IIb and VIa, such as CdS, ZnO and ZnS, or elements of groups Ib and VIIa. elements of groups IVa and VIa, such as PbS, PbO, SnS and PbSnTe, or elements of groups Va and VIa, such as Bi ₂ Te ₃ and Bi ₂ O ₃ , or elements of groups IIb and Va, such as Cd ₃ P ₂ , Zn ₃ P ₂ and Zn ₃ As ₂ , or elements of groups Ib and VIa, such as CuO, Cu ₂ O and Ag ₂ S, or elements of groups VIIIb and VIa, such as CoO, PdO, Fe ₂ O ₃ and NiO, or elements of groups VIb and VIa, such as MoS ₂ and WO ₃ , or elements of groups Vb and VIa, such as V ₂ O ₅ and Nbr ₂ O ₅ ; or elements of groups IVb and VIa, such as TiO ₂ and HfS ₂ ; or elements of groups IIIa and VIa. , for example _{In2O3 and In2S3} , or elements _{of group} VIa and _the lanthanides _{, such} as _Ce2O3 , _Pr2O3 , _{Sm2S3 , Tb2S3} and _La2S3 , or It may be composed of elements of group VIa and actinides, such as UO ₂ and UO ₃ .

Preferably, they contain at least one of the following metal oxides: titanium oxide, tungsten oxide, cerium oxide, bismuth oxide, zinc oxide, copper oxide, vanadium oxide, iron oxide, cadmium oxide, preferably: _TiO2 , _{Bi2O3 ,} CdO, _{Ce2O3 , CeO2} , _CeAlO3 , CuO _{, Fe2O3 , FeTiO3 , ZnFe2O3} , _V2O5 , ZnO, _{WO3 and ZnFe2O4} selected from, alone or in a mixture.

Semiconductor materials a, a' or at least one of semiconductor materials a, a' contain metal ions, particularly V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta. , Ti, or with one or more ions selected from non-metal ions, in particular C, N, S, F, P, or a mixture of metal and non-metal ions.

Semiconductor materials a, a' or at least one of semiconductor materials a, a' are group IVb, group Vb, group VIb, group VIIb, group VIIIb, group Ib, group IIb of the periodic table of elements, It may also contain one or more elements selected from the elements of group IIIa, group IVa and group Va in the metallic state, preferably in direct contact with said semiconductor material. It is preferentially a metal from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium.

It is noted that throughout this specification, groups of chemical elements are given according to the CAS IUPAC classification (CRC Handbook of Chemistry and Physics, publisher CRC Press, 81st edition, 2000-2001), rather than according to the new classification. Should. For example, Group VIII according to the CAS classification corresponds to Groups 8, 9 and 10 metals according to the new IUPAC classification.

The catalyst bed according to the invention can exhibit a thickness of at most 1 cm, especially at most 5 mm, and especially at least 10 μm. Preferably, the thickness is at least 100 or 200 microns. This thickness depends inter alia on the depth of penetration of the radiation from the irradiation source into the floor.

Another subject of the invention is a method for obtaining a catalyst bed as defined above, comprising mixing structured particles b of a mineral material, on the one hand, and particles of a semiconductor material a, on the other hand. The method consists in creating a uniform distribution of two types of particles within the bed. On both laboratory and industrial scales, screw mixer/mill type devices exist to ensure uniform mixing.

Another subject of the invention is a method for obtaining a catalyst bed as defined above, comprising the deposition on structured particles b of a mineral material of at least one of the semiconductor materials a, a' or the semiconductor materials a, a'. , by impregnating said structured particles with a solution of at least one precursor of a semiconductor material, or by ion exchange or by an electrochemical route, in particular of the type using molten salts, followed by drying and optional calcination. It's in the method of doing it. It is also possible to choose chemical vapor deposition (CVD), spray drying or atomic layer deposition (ALD), or any other technique known to the expert in this type of deposition. be.

Another subject of the invention is any reactor for the photocatalytic treatment of feedstocks in gaseous and/or liquid form, comprising at least one photocatalytic bed as defined above, said reactor A reactor that is installed in a fixed manner within a reactor. This is because the benefits of Mie scattering on structured particles can be best exploited when the bed is fixed (as opposed to a moving bed reactor).

Another subject of the invention is a method for the photocatalytic treatment of feedstocks in gaseous or liquid form, comprising:
- arranging at least one photocatalyst bed as defined above in a fixed manner within the reactor;
- contacting said feedstock with a catalyst bed in a reactor, and - applying to the photocatalyst bed, during the contacting operation, a wavelength in the UVA-A range and/or in the UV-B range and/or in the visible range, in particular in the wavelength range from 220 to 800 nm. , preferably by at least one radiation source emitting in the wavelength range from 300 to 750 nm.

Another subject of the invention is a method in which the photocatalytic treatment is:
- photooxidation of components present in the feedstock in liquid or gaseous form, specifically for the decontamination/decontamination of the feedstock, or - photocatalytic reduction of CO ₂ in the feedstock in liquid or gaseous form, or - Photolysis of feedstock water in liquid or gaseous form for the purpose of producing H2.

(List of drawings)
FIG. 1 shows a schematic re-emission pattern of an incident beam on a particle due to Rayleigh-type scattering and Mie-type scattering.

FIG. 2 shows a transmission electron microscopy (TEM) image of semiconductor particles made from titanium oxide used in accordance with embodiments of photocatalytic materials according to the present invention.

FIG. 3 shows a scanning electron microscopy (SEM) image of structured particles made from silicon oxide used in accordance with embodiments of photocatalytic materials according to the present invention.

FIG. 4 represents a simplified diagram of an installation aimed at measuring the performance quality of photocatalytic materials according to the invention.

FIG. 5 represents a graph quantifying the photocatalytic performance quality of two examples of materials according to the invention, with on the horizontal axis the fraction by volume of semiconductors made from titanium oxide of the materials according to the invention; The material of the invention comprises structured particles made of this semiconductor particle and silicon oxide and has, on the vertical axis, a total consumption of electrons over 20 hours per square meter, expressed in μmol/m ² .

(Description of embodiment)
The present invention relates to compositions of photocatalyst beds having mineral structured particles. The mineral structured particles, solid in this case, are calibrated according to the wavelength of the radiation emitted by the light source, activating the semiconductor material, where the radiation is large, and by utilizing Mie scattering the surface of these spheres is so that it is preferentially scattered in the direction of the radiation incident on it.

FIG. 1 therefore represents simply and diagrammatically the phenomenon of Mie scattering described above: on the left, a light source S emitting radiation of a given wavelength λ is symbolically represented. The diameter of the spherical particles P1 is not calibrated according to the invention and is less than 0.1λ. Spherical particles P1 reemit incident radiation fairly uniformly in all directions; this is Rayleigh scattering. On the other hand, the diameter of the particle P2 is calibrated to be between 0.1λ and 10λ, and the particle P2 advantageously re-emits radiation along the direction of the incident radiation; this is Mie scattering. This is what the present invention uses, so that the calibrated particles "guide" more radiation into the depth of the catalyst bed and facilitate its propagation, so that the semiconductor material is better used.

The semiconductor material combined with these particles then experiences a surprising increase in its photocatalytic activity. This activity can be utilized in all known fields of photocatalytic activity of liquid and/or gaseous fluids. It can be the reduction of _CO2 , the photocatalytic production of _H2 by photoconversion of water (also denoted by the term "water splitting"), or even the photocatalytic decontamination of air (conversion of VOCs) or photocatalytic decontamination of water. obtain.

The invention will be illustrated below by non-limiting examples using different photocatalytic materials and different structured particles.

(Photocatalyst material)
Photocatalyst material a1. The photocatalytic material a1 is titanium oxide: it is TiO ₂ available from Aldrich under the trade name Aerooxide® P25 and has a purity of 99.5%. Titanium oxide is in the form of fine particles. Its particle size is 21 nm as measured by transmission electron microscopy (TEM). Its specific surface area, determined by the BET method, is 52 m ² /g. BET is an abbreviation: it is Brunauer-Emmett- as defined in S. Brunauer, PH Emmett and E. Teller, J. Am. Chem.S oc., 1938, 60(2), pp 309-319. This is the Teller method.

Crystallographically, this titanium oxide is in the form of a mixture of rutile and anatase forms.

Figure 2 is a view obtained by TEM of these titanium oxide particles: it can be seen that they are of irregular shape and that they tend to agglomerate.

Photocatalyst material a2. Photocatalytic material a2 is titanium oxide doped with platinum metal particles prepared by photodeposition in the following way:
0.0712 g of H ₂ PtCl _{6.6H 2} O (37.5% by weight metal) is introduced into 500 mL of distilled water. Remove 50 mL of this solution and place in a jacketed glass reactor. 3 mL of methanol is then added with stirring, followed by 250 mg of TiO ₂ of type a1 (Aeroxide® P25, Aldrich®, purity >99.5%) to form a suspension.

The mixture is then left under UV irradiation for 2 hours with stirring. The lamp used to provide UV radiation is a 125W HPK® mercury vapor lamp. The mixture is then centrifuged at 3000 rpm for 10 minutes to collect the solids. This is followed by two wash operations with water, each of which is followed by centrifugation. Finally, the recovered powder is placed in an oven at 70° C. for 24 hours.

Thereby, photocatalyst material a2 is obtained. The content of Pt element is determined to be 0.99% by weight by inductively coupled plasma-atomic emission spectroscopy (ICP-AES).

Photocatalyst material a3. Photocatalytic material a3 is a commercially available semiconductor based on _WO3 (available from Sigma-Aldrich, exhibiting a particle size of less than 100 nm). The specific surface area, determined by the BET method, is equal to 20 m ² /g. The particle size of the photocatalytic material is 50±5 nm, as measured by X-ray diffraction (Debye-Scherrer method).

Photocatalyst material a4. Photocatalyst material a4 is a mixture of titanium oxide and copper oxide and platinum Cu ₂ O/Pt/TiO ₂ particles. It is prepared in the following way:
A solution of _Cu (NO ₃ ) ₂ was prepared by adding 0.125 g of Cu(NO ₃ ) 2.3H ₂ O (Sigma-Aldrich®, 98%) to 50 mL of a 50/50 isopropanol/H ₂ O mixture. That is, Cu ₂ + is dissolved in a solution having a concentration of 10.4 mmol/L.

The following was introduced into the reactor: 0.20 g of photocatalytic material a2, 25 mL of distilled water, and finally 25 mL of isopropanol. The system is purged in the dark under a flow of argon (100 mL/min) for 2 hours. The reactor is thermostatically controlled at 25° C. throughout the synthesis.

Subsequently, the argon flow is reduced to 30 mL/min and irradiation of the reaction mixture begins. The lamp used to provide UV radiation is a 125W HPK® mercury vapor lamp. Then 50 mL of copper nitrate solution are added to the mixture. The mixture is left under irradiation for 10 hours with stirring. The mixture is then centrifuged at 3000 rpm for 10 minutes to collect the solids. This is followed by two wash operations with water, each of which is followed by centrifugation. Finally, the recovered powder is placed in an oven at 70° C. for 24 hours.

Photocatalyst material a4, Cu ₂ O/Pt/TiO ₂ is obtained here. The content of Cu element is determined to be 2.2% by weight by ICP-AES. According to XPS (X-Ray Photoelectron Spectrometry) measurement, the copper oxide phase is 67% Cu ₂ O and 33% CuO.

(Structured particles)
Structured particles b1. The structured particles b1 chosen in some of the following examples are spherical particles made from commercially available SiO ₂ -based silicon oxide and can be obtained from Alfa Aesar (CAS:7631-86-9) : These are beads with a purity of greater than 99.9%, the average diameter of which is 0.4 μm, as determined by laser particle size analysis.

Figure 3 is a view obtained by SEM of these beads and it can indeed be seen that they are very uniform in their size and their shape.

Structured particles b2. The structured particles b2 chosen in another example are particles made from commercially available SiO ₂ based silicon oxide, which can be obtained from Sigma-Aldrich under the commercial reference Davisil Grade 710, 10-14 μm. : These are beads with a purity of >99%, the average size of which is 12.7 μm (distribution by volume), as determined by laser particle size analysis.

Semiconductor particles a1-a4 and structured particles b1 (SiO ₂ powder) or b2 (SiO ₂ powder with a particle size larger than the particle size of b1) at a dilution rate varying between 0% and 75% by volume. Mix mechanically to obtain a uniform distribution of the two types of particles in the material. In the sense of the present invention, "dilution factor" is equal to the ratio of the volume occupied by structured particles made of mineral material to the volume occupied by the sum of semiconductor material(s) and structured particles. is recalled.

Subsequently, as shown in Figure 4, each sample (3) of the photocatalytic material of each example is subjected to a test for photocatalytic reduction of _CO2 in the gas phase in the following manner: a continuously operated reactor. (1), horizontally placing a fixed bed (2) in the cavity, the bed containing the sintered material (4), and placing the sample (3) on the sintered material (4). is placed. The reactor (1) has in its upper wall an optical window (5) made of quartz, facing the sample (3). Above the reactor, facing the window (5), a UV-visible radiation source (6) is arranged.

During operation, the reactor (1) is fed with a stream of gaseous CO ₂ (7) via the upper inlet, which stream has been previously bubbled in a vessel/saturator filled with water (8). has been done. The stream (7) passes through the sample (3) and is then discharged via an outlet in the lower part in the form of a stream (9), which stream (9) is passed through a gas analyzer (10) of the micro gas chromatograph type. is analyzed inline by

The UV-visible radiation source (6) is a xenon lamp available from Asahi under the trade name MAX303.

The tests were carried out on samples (3) in an amount of 45-70 mg, the weight of which varies depending on their chosen dilution, the thickness of the catalyst bed (2) and therefore the sample (3). The thickness of remains fixed and equal to 0.3 mm.

The operating conditions are as follows:
- Ambient temperature - Atmospheric pressure - Flow rate (7) of CO ₂ through the water saturator (8): 18 mL/h
- Duration of test for each sample: 20h
- Irradiation output of the xenon lamp (6): kept constant at 80 W/m ² and measured in the wavelength range of 315-400 nm.

The target conversion of _CO2 corresponds to the following reaction.

Determination of the photocatalytic performance quality of the samples was carried out by microchromatography with a device (10), and the production of H ₂ , CH ₄ and CO resulting from the reduction of CO ₂ and H ₂ O was monitored by analysis every 6 minutes. Ru. Products of the reduction of CO ₂ are identified, such as CO, methane and even ethane. The average photocatalytic activity is expressed in μmol of photogenerated electrons consumed by the reaction per square meter of irradiated catalyst surface area over the duration of the test.

(Example)
All of the examples performed and their results are shown in Table 1 below.

From this table, it can be seen that the photocatalytic activity of the "mixed" material combining semiconductor material and structured particles according to the invention is very significantly higher than the photocatalytic activity of the material consisting only of semiconductor material, which is responsible for the photocatalytic activity of the material. It is found that

Comparing the results of Example 1 (comparative example) and Example 2, it can be seen that when the amount of semiconductor material is reduced by 25% (Example 2), the photocatalytic activity jumps up to 4.5 times. Starting from another semiconductor (materials a2, a3, a4), the photocatalytic activity at the "start" is higher for the material made of 100% semiconductor, and the present invention shows that by combining it with structured particles , it can be increased by at least 4 times: Example 9 therefore achieves an excellent level of photocatalytic activity.

FIG. 5 depicts the results of Examples 2 and 3 in graphical form. The volume fraction of particles made from TiO ₂ is shown on the horizontal axis and the total consumption of electrons per square meter over 20 hours is shown on the vertical axis. From this figure, it can be seen that Example 3 (diamond in the graph), in which the structured particle b2 is too large in size, is different from Example 2 (circle in the graph), which uses structured particles b1 whose size is calibrated to be advantageous for Mie scattering. ) shows much inferior results.

This calibration of structured particles is simple to select and obtain, and is significantly easier than having to refine other parameters where controlling the macro- or micro-porosity of the material type is more complex.

It will be appreciated that the invention is very flexible in its implementation: depending on the desired level of performance, the choice of materials, the dilution ratio and the It would be possible to adapt the composition of the materials according to the invention by varying the way in which the mixing between them would be carried out (mechanical mixing, chemical or physico-chemical integration, etc.).

Figure 2 shows a schematic re-emission pattern of an incident beam on a particle due to Rayleigh-type scattering and Mie-type scattering. Figure 2 shows a transmission electron microscopy (TEM) image of semiconductor particles made from titanium oxide used in accordance with an embodiment of a photocatalytic material according to the present invention. Figure 3 shows a scanning electron microscopy (SEM) image of structured particles made from silicon oxide used in accordance with an embodiment of a photocatalytic material according to the present invention. 1 represents a simplified diagram of an installation aimed at determining the performance quality of photocatalytic materials according to the invention; FIG. Represents a graph quantifying the photocatalytic performance quality of two examples of materials according to the invention, with on the horizontal axis the fraction by volume of the semiconductor made from titanium oxide of the materials of the invention and on the vertical axis , with a total consumption of electrons over 20 hours per square meter, expressed in μmol/m ² .

Claims (15)

A catalyst bed comprising a particulate photocatalytic catalyst, said bed comprising structured particles b made of mineral material, said structured particles in combination with at least one semiconductor material a having photocatalytic properties. and this combination is:
- mixing structured particles b made of mineral material with semiconductor material a in the form of particles; and/or - chemical or physical mixing of semiconductor material a on structured particles b made of mineral material; caused by chemical deposition;
Catalyst bed characterized in that the structured particles b are essentially spherical and have an average diameter of 22 nm to 8.0 μm, preferably 30 nm to 7.5 μm. A catalyst bed according to claim 1, characterized in that all of the particles in the bed are randomly arranged. 2. If the bed contains the semiconductor material a in the form of particles, said particles a exhibit an average size of at most 100 nm, in particular at most 50 nm and at least 5 nm, preferably from 10 to 30 nm. 2. The catalyst bed according to 2. characterized in that it exhibits a porosity equal to the ratio of the void volume in the photocatalyst bed to the total volume of the photocatalyst bed composed of voids and particles: a minimum of 40% and preferably a maximum of 80%, in particular from 40% to 70%. Catalyst bed according to any one of claims 1 to 3, characterized in that: Particularly in the case of chemical or physicochemical deposition of a semiconductor material a on structured particles b made of a mineral material, the volume occupied by the structured particles b made of a mineral material versus the semiconductor material (one or plural types) "dilution factor" equal to the ratio of the volume occupied by the sum of a, a' and structured particles b made of mineral material: up to 80%, in particular from 5% to 70%, preferably from 10% to 50% Catalyst bed according to any one of claims 1 to 4, characterized in that it shows %. comprising at least two different semiconductor materials, a first material a and a second material a'. Catalyst bed according to any one of claims 1 to 5, characterized in that it is produced by:
- mixing structured particles b made of mineral material with semiconductor material(s) in the form of particles of a first material a and particles of a second material a', respectively; /or,
- chemical or physicochemical deposition of the semiconductor material a, a' on the carrier particles b; deposition or structuring of both the first semiconductor material a and the second semiconductor material a' on the structured particles b; Either by depositing a first semiconductor material a on a first part of the particle b and by depositing a second semiconductor material a' on a second part of the structured particle b. The structured particles b made from mineral materials are made from metal oxide(s), in particular from oxides of metals of groups IIIa and IVa of the periodic table, preferably aluminum oxide, oxide Catalyst bed according to any one of claims 1 to 6, characterized in that it is selected from silicon, aluminum and a mixture of oxides of silicon. At least one of the semiconductor materials a, a' or the semiconductor materials a, a' is a metal oxide of the following: titanium oxide, tungsten oxide, cerium oxide, bismuth oxide, zinc oxide, copper oxide, vanadium oxide, iron oxide, Contains at least one kind of cadmium oxide, preferably TiO ₂ , Bi ₂ O ₃ , CdO, Ce ₂ O ₃ , CeO ₂ , CeAlO ₃ , CuO, Fe ₂ O ₃ , FeTiO ₃ , ZnFe ₂ O ₃ , Catalyst bed according to any one of claims 1 to 7, characterized in that it is selected from V ₂ O ₅ , ZnO, WO ₃ and ZnFe ₂ O ₄ , alone or in a mixture. Semiconductor materials a, a' or at least one of semiconductor materials a, a' contain metal ions, particularly V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta. , Ti or with one or more ions selected from non-metallic ions, in particular C, N, S, F, P or mixtures of metallic and non-metallic ions. Catalyst bed according to any one of claims 1 to 8. Semiconductor materials a, a' or at least one of semiconductor materials a, a' are group IVb, group Vb, group VIb, group VIIb, group VIIIb, group Ib, group IIb of the periodic table of elements, It also contains one or more elements in the metallic state selected from the elements of group IIIa, group IVa and group Va, in direct contact with said semiconductor material, preferably platinum, palladium, Catalyst bed according to any one of claims 1 to 9, characterized in that it is selected from gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium. A method for obtaining a catalyst bed according to any one of claims 1 to 10, comprising mixing structured particles b of the mineral material on the one hand and particles of the semiconductor material a on the other hand. A method characterized in that a homogeneous distribution of two types of particles is produced in the bed. 11. A method for obtaining a catalyst bed according to any one of claims 1 to 10, comprising structured particles b of a mineral material of at least one of the semiconductor materials a, a' or the semiconductor materials a, a'. Deposition is carried out by impregnating said structured particles with a solution of at least one precursor of a semiconductor material, by ion exchange or by an electrochemical route, in particular of the type using molten salts, followed by drying and optional calcination. A method characterized in that it is carried out by chemical vapor deposition, by spray drying or by atomic layer deposition. Reactor (1) for the photocatalytic treatment of feedstocks in gaseous or liquid form, comprising at least one photocatalyst bed (2) according to any one of claims 1 to 10, A reactor mounted in a fixed manner within said reactor. A method for the photocatalytic treatment of feedstocks (7) in gaseous and/or liquid form, characterized in that:
- arranging at least one photocatalyst bed (2) according to any one of claims 1 to 10 in a fixed manner in the reactor (1);
- contacting said feedstock (7) with a catalyst bed (2) in a reactor, and - the photocatalyst bed (2) being exposed to UV-A range and/or UV-B range and/or visible radiation during the contacting operation. irradiation by at least one radiation source (6) emitting in the wavelength range, in particular in the wavelength range from 220 to 800 nm, preferably in the wavelength range from 300 to 750 nm. The method according to claim 14, characterized in that the photocatalytic treatment is as follows:
- photooxidation of components present in the feedstock in liquid or gaseous form, specifically for the decontamination/decontamination of the feedstock, or - photocatalytic reduction of CO ₂ in the feedstock in liquid or gaseous form, or - Photolysis of liquid or gaseous feedstock water with the purpose of producing _H2 .

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